Pressure measurements are central to monitoring the status of many physiological functions and, thus, to the monitoring of the progress of many diseases. Such pressure measurements as arterial and venous blood pressures, intra-cranial fluid pressure, or transpulmonary airway pressure all use devices that measure pressures in a range greater than 4 cm H2O. Such devices typically use narrow bore tubing to transduce the pressure from the region of interest to the pressure sensor outside the body, or use fiber-optics to transmit and receive light reflected from a pressure-sensitive device such as a diaphragm located at the tip. The use of narrow bore tubing introduces multiple artifacts into the measurements, especially when the frequency of the measured signal is high and when the volume of the “cavity” where the pressure to be determined is low. Current fiber-optics based systems, utilizing either a single detecting fiber or a bundle of fibers whose detecting tips are set at a single fixed distance from the displacement diaphragm, are not sensitive enough to detect the small (less than 2 cm H2O) rapidly changing pressures that are the goal of this invention. No system or method is currently available that can reliably measure artifact-free dynamic pressures in the range less than 10 cm H2O with high resolution in small confined body spaces, as for example, those of the dimensions of the rat trachea. For detailed analysis of, e.g., pulmonary function in small animals, it is necessary to monitor pressures in the range 0-10 cm H2O, with a resolution of 0.1 mm H2O. For such small laboratory animals as the rat, the diameter of the probe must be less than 3 mm. The system must also be electrically isolated and immune from environmental electrical and magnetic interference, have a large signal-to-noise ratio, and a wide dynamic range suitable for both normal and pathological conditions.
Accordingly, there is a need for an improved system and method for dynamically monitoring ultra-low pressures in the range 0-10 cm H2O, with a resolution of 0.1 mm H2O in confined spaces less than 3 mm in diameter. The present invention meets all these criteria.
The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the invention and, together with descriptions, serve to explain the principles of the invention. They are not intended to limit the scope of the invention to the embodiments described. It is appreciated that various changes and modifications can be made without departing from the spirit and scope of the invention as defined in the appended claims.